Various different types of power tools are known having a substantial portion of their outer casing formed from plastics material instead of metal in order to make the tool lighter and much easier to handle as well as being cheaper to produce and safer to use. Additionally, plastics material housings have advantages in that the tools can be made to look more aesthetically pleasing and free from sharp corners, and since the plastics material can be self-coloured by the addition of appropriate pigments to the polymeric material, painting is not necessary, so that the tool will retain a good appearance for the majority of its working life.
However, the disadvantage of a plastics material housing is that since the moving parts of the power tool can generate a considerable amount of heat, steps have to be taken in the design to ensure that the plastics material casing is protected from excessive heat, and various attempts have been made to overcome or avoid this problem.
In one example, it is known to provide a power tool having a metal casing, which is then coated in plastics material to give the appearance of the casing being made of plastics material while avoiding the problem of over-heating the plastics material. However such a solution is not particularly advantageous since it merely replaces the normal paint layer with a plastics material layer for the sake of appearances, the tool itself being basically unchanged and still having the disadvantages of being relatively heavy and more expensive to produce.
In German Gebrauchsmuster No. 6,929,672, there is disclosed a hand tool having a deformable plastics material barrel in which a metal tube is inserted for receiving the mechanism of the tool and providing the main strength of the barrel in use. In German Offenlegungschrift No. 2,533,284, a power tool is shown having a plastics material housing having a metal insert member incorporated therein for receiving a bearing in which the output spindle of the power tool is supported. Similarly, German Patent Specification No. 1,427,729 shows a power tool having a steel bushing provided in the front end of a plastics material housing of the power tool, which steel bushing has ratchet teeth provided thereon for enabling the tool to be utilised in a hammer drill mode. United Kingdom Patent Specification No. 1,560,420 discloses a metal sleeve in the plastic casing of a hammer drill. These arrangements indicate the basic idea of utilising a metal insert in a plastics material housing for the purpose of reinforcing the housing and for supporting or forming part of the mechanism of the power tool.
However, such known prior art arrangements have the disadvantages that they firstly require cast and/or machined metal inserts which generally have to be machined with precision and which are relatively expensive to produce. An assembly involves fitting the machined inserts into a pre-molded plastics material housing, which complicates assembly, and can increase manufacturing costs of assembly. Further, due to the heat generated during operation of the tool, problems can arise due to over-heating which can damage the plastics material housing and gradually loosen the metal insert therein, eventually resulting in a shortened working life of the tool; to avoid this, resort must often be made to bulkier components to dissipate the heat to avoid damage to the plastics material housing.
United Kingdom Patent Application No. 2,050,213 discloses a power tool having a load bearing structural foam housing closely surrounding a thin wall inner housing having improved heat conductivity in the region of the bearings. However, this inner housing encloses and extends around all the components of the power tool, and after the tool and the inner housing have been assembled, the outer foam housing has to be moulded around the assembled tool.